Spondylolysis is a unilateral or bilateral defect in the region of the pars interarticularis, which may or may not be accompanied by the vertebral body slippage. It is most commonly the sequelae of repetitive trauma to the growing immature skeletal architecture among a genetically susceptible individuals.  The pars interarticularis is considered the isthmus or bone bridge between the inferior and superior articular surfaces of a single vertebra. 
Spondylolysis may be congenital or acquired. Although the exact pathogenesis remains unknown in all cases, it is most commonly secondary to a fatigue or stress fracture of the pars interarticularis that persists as a non-union. It typically develops in genetically susceptible children and adolescents with faulty biomechanics, and who also experience repetitive microtrauma on the pars interarticularis from repeated activities involving lumbar hyperextension with rotation.
The prevalence of spondylolysis is 4% by age 6 and 6% by age 14 and thereafter remains constant throughout adulthood.
There is a genetic predisposition with an increased incidence seen in:
Adolescents involved in sports have a higher prevalence compared to those not involved in sports. The mean age of diagnosis is 15 years of age.
There is an increased incidence among participants of certain higher-risk sports which involve repeated axial loading and/or lumbar hyperextension with rotation. These sports include gymnastics, dance, football (particularly linemen), rugby, wrestling, martial arts, soccer, basketball, cheerleading, pitching, golf, tennis, volleyball servers, weightlifting, and butterfly and breaststroke swimming.
Ninety percent of the cases of spondylolysis occur at the L5 vertebra with decreasing incidence at progressively higher lumbar levels. Excessive lumbar lordosis is a risk factor for spondylolysis development. Most commonly, pars interarticularis defects occur bilaterally as opposed to unilaterally. Unhealed pars interarticularis defects may progress to lytic (isthmic) spondylolisthesis, which is an anterior displacement of the vertebral body in relation to the vertebra below. It is important to note unilateral lesions never progress to spondylolisthesis. However, in patients with bilateral spondylolysis, at the time of diagnosis, 50% to 75% will already have accompanying spondylolisthesis. Slip progression is more common in adolescents compared to adults, and although the incidence of spondylolysis is more common in males, the slip progression of spondylolisthesis occurs more frequently in females.
Additionally, multifidi muscles of the back attach to the mamillary process of the vertebra thereby stabilizing vertebral joints and providing stability at each segmental level. The mammillary process is not completely formed until 25 years of age. Full ossification of the neural arch is also not completed until the same age limit. These 2 factors play a pivotal role in the development of the condition during adolescence.
Spondylolysis mostly remains asymptomatic, but approximately 10% of affected individuals manifest symptoms constituting of insidious onset, recurrent axial low back pain that increases with activity, is exacerbated by lumbar hyperextension, and may or may not be associated with a radicular component. The pain can range from mild to severe in intensity and is described as a dull, aching pain in the lower back, buttocks, and posterior thigh regions. If neurologic symptoms/signs are present, it is likely secondary to spondylolysis with spondylolisthesis or associated degenerative processes resulting in narrowing of the neuroforamina and the spinal nerve impingements. Since spondylolysis most commonly affects L5 on S1, the corresponding dermatomal and myotomal pattern clinical manifestations usually occur. It is important to note that if the patient’s spondylolysis has progressed to spondylolisthesis and they are presenting with pain, the degree of pain does not correlate with the degree of slippage, and this presents a diagnostic challenge and explains why the condition is often advanced at the time of diagnosis.
Neurological examination would specifically show increased lumbar lordosis, tight hamstrings, reduced trunk range of motion (particularly with extension), tenderness to palpation overlying the pars fracture site, a positive stork test (single leg hyperextension and rotation of the spine which reproduces the patient pain and is diagnostic of spondylolysis until proven otherwise), with the characteristic abscence of any radiculopathy. Again, radicular symptoms can occur, but they are uncommon.
As a general consensus rule, a patient's neurologic examination, as well as all laboratory evaluations including inflammatory markers, will be largely unremarkable.
There is no universally accepted guidelines for an imaging protocol, but the initial imaging studies of choice when the condition is suspected are plain radiographs in the posteroanterior, lateral, and oblique views of the lumbosacral region in the standing position. When present, the lesion is most typically visible in the oblique view which shows the classic "collar on the Scotty dog" and represents the bony defect between the inferior articular surface and the superior articular surface of a single vertebra. As with any stress fracture, plain films may miss the lesion within the first 2 weeks of the injury. Additionally, it ihas been reported that plain radiographs only have a sensitivity of 33% in detecting spondylolysis. Some authorities advocate axial CT-imaging as the test of choice for spondylolysis; however, due to the high prevalence of spondylolysis in the pediatric population and concerns regarding unnecessary radiation exposure, the next advanced imaging modality typically chosen, if plain films are negative, is the MRI. MRI is excellent at detecting bone marrow edema associated with acute pars interarticularis stress injury as well as detailing neural and soft tissue pathologies. The SPECT scan is a suitable alternative to MRI for detecting acute stress fractures and is also useful in determining the acuity of a fracture. It however carries the risk of concurrent radiation hazards, which is therefore preferably avoided in pediatric population.
Most patients with spondylolysis, including athletes, can be managed conservatively. In fact, patients who are asymptomatic and their condition is discovered incidentally on imaging may maintain their current level of physical activity without any activity restrictions. However, if the patient presents with acute symptomatic spondylolysis as confirmed by SPECT-scan or MRI, conservative treatments are warranted and would include:
Adjunctive treatments including ice/heat therapy, NSAIDS, epidural steroid injections, massage, osteopathic or chiropractic manipulation, and cognitive-behavioral therapy (CBT) are generally well-tolerated, are of benefits, and should be considered.
With conservative treatment protocol, 75% of adolescents will improve, and invariably their lytic defects heal. Unilateral defects are more likely to heal than bilateral defects. In cases of spondylolysis with concomitant spondylolisthesis, the bony defects are unlikely to heal but the implementation of the same conservative treatment principles typically results in an abatement of the patients’ symptomatology and return to their previous level of activity. A recent randomized control trial found no difference in the clinical outcomes among patients with spondylolisthesis among cohorts treated conservatively with those managed surgically; which is clinically significant considering the cost and the potential complications associated with surgical treatments. Additionally, there is currently no clinical evidence favoring spinal bracing in preventing vertebral slippage among patients with spondylolysis and spondylolisthesis.
Surgical intervention is only warranted if the patient fails a conservative management trial of at least 6 months or has progressive neurologic symptoms with saddle anesthesia, bowel/bladder dysfunction, refractory pain, or develop spondylolisthesis of grade 3 or higher. The most commonly performed surgical treatments of spondylolysis include a direct repair of the defect in the pars interarticularis at L1 to L4 levels, and an inter-transverse fusion for defects at the L5 level.
The prognosis in patients with spondylolysis is usually excellent. Asymptomatic individuals require no specific treatments or any modifications to activities of daily living or athletic activities. Even patients who present with symptomatic spondylolysis usually have a very favourable prognosis as validated by a recent meta-analysis which demonstrated that the 92% of the adolescent athletes were able to return to competitions when they are treated conservatively, and 90% of the time when managed surgically.
In the majority of patients with spondylolysis, the condition is occult and remains asymptomatic throughout their lifetimes. However, degenerative disc disease and resultant spondylosis, that typically occurs as a sequelae of the aging process, has a propensity to be accelerated in patients with spondylolysis. This may lead to spinal stenosis and lumbar radiculopathies. These deleterious effects may also occur secondary to vertebral body slippage in almost 50% to 75% of patients with bilateral spondylolysis. Potential surgical complications would include a failed fusion, infections, chronic persistent pain, neurological deteriorations, and the failed back surgery syndrome.
The need for surgical correction of spondylolysis is uncommon. However, if surgical correction is justified, the postoperative rehabilitative processes should include stringent protection of the surgical site until wound closure (bracing is typically surgeon dependent), proper analgesia, graded physical therapy, and education on proper biomechanics with an emphasis on maintaining corrective postures and sleeping positionings.
Asymptomatic individuals, whose condition is discovered incidentally on imaging, should be reassured of the generally benign course of the disease throughout their lifetime, without any need for activity restrictions. However, symptomatic individuals with a pars interarticularis defect that is actively undergoing treatment, regardless of whether the treatment is conservative or surgical, need to have an education and understanding on proper biomechanics to optimize their comfort as well as to decrease stress and promote healing of the involved structures. Techniques which should be taught and implemented include:
Spondylolysis is best managed by an interprofessional team that includes a surgeon, primary care provider, physical therapist, nurse, and a sports physician. The majority of patients are managed conservatively.
Surgical correction of spondylolysis is uncommon. However, if surgical correction is necessary the postoperative rehabilitative care should include protection of the surgical site until wound closure (bracing is typically surgeon dependent), proper analgesia, physical therapy, and education on proper biomechanics with an emphasis on posture and sleeping positioning. An integral part of the postoperative rehabilitative care of athletes constitutes a graded return to sports protocol, comprising of education on maintaining proper biomechanics at first, and gradually progressing to sport specific activities as tolerated.
For those who remain compliant with physical therapy, the prognosis is good. Those who continue to lead a sedentary lifestyle usually develop chronic refractory pain and the resultant poor quality of life.
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